Installation

If you plan to use delayed_job with Active Record, add delayed_job_active_record to your Gemfile.

gem'delayed_job_active_record'

If you plan to use delayed_job with Mongoid, add delayed_job_mongoid to your Gemfile.

gem'delayed_job_mongoid'

Run bundle install to install the backend and delayed_job gems.

The Active Record backend requires a jobs table. You can create that table by
running the following command:

railsgeneratedelayed_job:active_recordrakedb:migrate

Development

In development mode, if you are using Rails 3.1+, your application code will automatically reload every 100 jobs or when the queue finishes.
You no longer need to restart Delayed Job every time you update your code in development.

Rails 4

If you are using the protected_attributes gem, it must appear before delayed_job in your gemfile.

Upgrading from 2.x to 3.0.0 on Active Record

Delayed Job 3.0.0 introduces a new column to the delayed_jobs table.

If you're upgrading from Delayed Job 2.x, run the upgrade generator to create a migration to add the column.

railsgeneratedelayed_job:upgraderakedb:migrate

Queuing Jobs

Call .delay.method(params) on any object and it will be processed in the background.

handle_asynchronously can take as options anything you can pass to delay. In
addition, the values can be Proc objects allowing call time evaluation of the
value. For some examples:

classLongTasksdefsend_mailer# Some other code
endhandle_asynchronously:send_mailer,:priority=>20defin_the_future# Some other code
end# 5.minutes.from_now will be evaluated when in_the_future is called
handle_asynchronously:in_the_future,:run_at=>Proc.new{5.minutes.from_now}defself.when_to_run2.hours.from_nowendclass<<selfdefcall_a_class_method# Some other code
endhandle_asynchronously:call_a_class_method,:run_at=>Proc.new{when_to_run}endattr_reader:how_importantdefcall_an_instance_method# Some other code
endhandle_asynchronously:call_an_instance_method,:priority=>Proc.new{|i|i.how_important}end

If you ever want to call a handle_asynchronously'd method without Delayed Job, for instance while debugging something at the console, just add _without_delay to the method name. For instance, if your original method was foo, then call foo_without_delay.

Rails 3 Mailers

Due to how mailers are implemented in Rails 3, we had to do a little work around to get delayed_job to work.

# without delayed_job
Notifier.signup(@user).deliver# with delayed_job
Notifier.delay.signup(@user)# with delayed_job running at a specific time
Notifier.delay(run_at:5.minutes.from_now).signup(@user)

Remove the .deliver method to make it work. It's not ideal, but it's the best
we could do for now.

Named Queues

DJ 3 introduces Resque-style named queues while still retaining DJ-style
priority. The goal is to provide a system for grouping tasks to be worked by
separate pools of workers, which may be scaled and controlled individually.

Running Jobs

script/delayed_job can be used to manage a background process which will
start working off jobs.

To do so, add gem "daemons" to your Gemfile and make sure you've run rails
generate delayed_job.

You can then do the following:

RAILS_ENV=production script/delayed_job start
RAILS_ENV=production script/delayed_job stop
# Runs two workers in separate processes.
RAILS_ENV=production script/delayed_job -n 2 start
RAILS_ENV=production script/delayed_job stop
# Set the --queue or --queues option to work from a particular queue.
RAILS_ENV=production script/delayed_job --queue=tracking start
RAILS_ENV=production script/delayed_job --queues=mailers,tasks start
# Use the --pool option to specify a worker pool. You can use this option multiple times to start different numbers of workers for different queues.
# The following command will start 1 worker for the tracking queue,
# 2 workers for the mailers and tasks queues, and 2 workers for any jobs:
RAILS_ENV=production script/delayed_job --pool=tracking --pool=mailers,tasks:2 --pool=*:2 start
# Runs all available jobs and then exits
RAILS_ENV=production script/delayed_job start --exit-on-complete
# or to run in the foreground
RAILS_ENV=production script/delayed_job run --exit-on-complete

Rails 4:replace script/delayed_job with bin/delayed_job

Workers can be running on any computer, as long as they have access to the
database and their clock is in sync. Keep in mind that each worker will check
the database at least every 5 seconds.

You can also invoke rake jobs:work which will start working off jobs. You can
cancel the rake task with CTRL-C.

If you want to just run all available jobs and exit you can use rake jobs:workoff

Work off queues by setting the QUEUE or QUEUES environment variable.

QUEUE=tracking rake jobs:work
QUEUES=mailers,tasks rake jobs:work

Restarting delayed_job

The following syntax will restart delayed jobs:

RAILS_ENV=production script/delayed_job restart

To restart multiple delayed_job workers:

RAILS_ENV=production script/delayed_job -n2 restart

Rails 4:replace script/delayed_job with bin/delayed_job

Custom Jobs

Jobs are simple ruby objects with a method called perform. Any object which responds to perform can be stuffed into the jobs table. Job objects are serialized to yaml so that they can later be resurrected by the job runner.

To set a per-job max run time that overrides the Delayed::Worker.max_run_time you can define a max_run_time method on the job

NOTE: this can ONLY be used to set a max_run_time that is lower than Delayed::Worker.max_run_time. Otherwise the lock on the job would expire and another worker would start the working on the in progress job.

Gory Details

The library revolves around a delayed_jobs table which looks as follows:

create_table:delayed_jobs,:force=>truedo|table|table.integer:priority,:default=>0# Allows some jobs to jump to the front of the queue
table.integer:attempts,:default=>0# Provides for retries, but still fail eventually.
table.text:handler# YAML-encoded string of the object that will do work
table.text:last_error# reason for last failure (See Note below)
table.datetime:run_at# When to run. Could be Time.zone.now for immediately, or sometime in the future.
table.datetime:locked_at# Set when a client is working on this object
table.datetime:failed_at# Set when all retries have failed (actually, by default, the record is deleted instead)
table.string:locked_by# Who is working on this object (if locked)
table.string:queue# The name of the queue this job is in
table.timestampsend

On error, the job is scheduled again in 5 seconds + N ** 4, where N is the number of attempts or using the job's defined reschedule_at method.

The default Worker.max_attempts is 25. After this, the job either deleted (default), or left in the database with "failed_at" set.
With the default of 25 attempts, the last retry will be 20 days later, with the last interval being almost 100 hours.

The default Worker.max_run_time is 4.hours. If your job takes longer than that, another computer could pick it up. It's up to you to
make sure your job doesn't exceed this time. You should set this to the longest time you think the job could take.

By default, it will delete failed jobs (and it always deletes successful jobs). If you want to keep failed jobs, set
Delayed::Worker.destroy_failed_jobs = false. The failed jobs will be marked with non-null failed_at.

By default all jobs are scheduled with priority = 0, which is top priority. You can change this by setting Delayed::Worker.default_priority to something else. Lower numbers have higher priority.

The default behavior is to read 5 jobs from the queue when finding an available job. You can configure this by setting Delayed::Worker.read_ahead.

By default all jobs will be queued without a named queue. A default named queue can be specified by using Delayed::Worker.default_queue_name.

It is possible to disable delayed jobs for testing purposes. Set Delayed::Worker.delay_jobs = false to execute all jobs realtime.

You may need to raise exceptions on SIGTERM signals, Delayed::Worker.raise_signal_exceptions = :term will cause the worker to raise a SignalException causing the running job to abort and be unlocked, which makes the job available to other workers. The default for this option is false.